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排序方式: 共有450条查询结果,搜索用时 15 毫秒
91.
Coral Falco Octavio Alvarez Isabel Castillo Isaac Estevan Julio Martos Fernando Mugarra Antonio Iradi 《Journal of biomechanics》2009,42(3):242-248
Taekwondo, originally a Korean martial art, is well known for its kicks. One of the most frequently used kicks in competition is Bandal Chagui or roundhouse kick. Excellence in Taekwondo relies on the ability to make contact with the opponent's trunk or face with enough force in as little time as possible, while at the same time avoiding being hit. Thus, the distance between contestants is an important variable to be taken into consideration. Thirty-one Taekwondo athletes in two different groups (expert and novice, according to experience in competition) took part in this study. The purpose of this study was to examine both impact force and execution time in a Bandal Chagui or roundhouse kick, and to explore the effect of execution distance in these two variables. A new model was developed in order to measure the force exerted by the body on a load. A force platform and a contact platform were used to measure these variables. The results showed that there are no significant differences in terms of impact force in relation to execution distance in expert competitors. Significant and positive correlations between body mass and impact force (p<.01) seem to mean that novice competitors use their body mass to generate high impact forces. Significant differences were found in competitive experience and execution time for the three different distances of kicking considered in the study. Standing at a certain further distance from the opponent should be an advantage for competitors who are used to kick from a further distance in their training. 相似文献
92.
Octavio Perez‐Garcia Luz E. De‐Bashan Juan‐Pablo Hernandez Yoav Bashan 《Journal of phycology》2010,46(4):800-812
Heterotrophic growth of microalgae presents significant economic advantages over the more common autotrophic cultivation. The efficiency of growth and nitrogen, phosphorus, and glucose uptake from synthetic wastewater was compared under heterotrophic, autotrophic, and mixotrophic regimes of Chlorella vulgaris Beij. immobilized in alginate beads, either alone or with the bacterium Azospirillum brasilense. Heterotrophic cultivation of C. vulgaris growing alone was superior to autotrophic cultivation. The added bacteria enhanced growth only under autotrophic and mixotrophic cultivations. Uptake of ammonium by the culture, yield of cells per ammonium unit, and total volumetric productivity of the culture were the highest under heterotrophic conditions when the microalga grew without the bacterium. Uptake of phosphate was higher under autotrophic conditions and similar under the other two regimes. Positive influence of the addition of A. brasilense was found only when light was supplied (autotrophic and mixotrophic), where affinity to phosphate and yield per phosphate unit were the highest under heterotrophic conditions. The pH of the culture was significantly reduced in all regimes where glucose was consumed, similarly in heterotrophic and mixotrophic cultures. It was concluded that the heterotrophic regime, using glucose, is superior to autotrophic and mixotrophic regimes for the uptake of ammonium and phosphate. Addition of A. brasilense positively affects the nutrient uptake only in the two regimes supplied with light. 相似文献
93.
Norma A Valdez-Cruz Luis Caspeta Néstor O Pérez Octavio T Ramírez Mauricio A Trujillo-Roldán 《Microbial cell factories》2010,9(1):18
The temperature inducible expression system, based on the pL and/or pR phage lambda promoters regulated by the thermolabile
cI857 repressor has been widely use to produce recombinant proteins in prokariotic cells. In this expression system, induction
of heterologous protein is achieved by increasing the culture temperature, generally above 37°C. Concomitant to the overexpression
of heterologous protein, the increase in temperature also causes a variety of complex stress responses. Many studies have
reported the use of such temperature inducible expression system, however only few discuss the simultaneous stress effects
caused by recombinant protein production and the up-shift in temperature. Understanding the integral effect of such responses
should be useful to develop improved strategies for high yield protein production and recovery. Here, we describe the current
status of the heat inducible expression system based on the pL and/or pR λ phage promoters, focusing on recent developments
on expression vehicles, the stress responses at the molecular and physiological level that occur after heat induction, and
bioprocessing factors that affect protein overexpression, including culture operation variables and induction strategies. 相似文献
94.
Pia Aravena Esteban Hurtado Rodrigo Riveros Juan Felipe Cardona Facundo Manes Agustín Ibá?ez 《PloS one》2010,5(7)
Background
Behavioral studies have provided evidence for an action–sentence compatibility effect (ACE) that suggests a coupling of motor mechanisms and action-sentence comprehension. When both processes are concurrent, the action sentence primes the actual movement, and simultaneously, the action affects comprehension. The aim of the present study was to investigate brain markers of bidirectional impact of language comprehension and motor processes.Methodology/Principal Findings
Participants listened to sentences describing an action that involved an open hand, a closed hand, or no manual action. Each participant was asked to press a button to indicate his/her understanding of the sentence. Each participant was assigned a hand-shape, either closed or open, which had to be used to activate the button. There were two groups (depending on the assigned hand-shape) and three categories (compatible, incompatible and neutral) defined according to the compatibility between the response and the sentence. ACEs were found in both groups. Brain markers of semantic processing exhibited an N400-like component around the Cz electrode position. This component distinguishes between compatible and incompatible, with a greater negative deflection for incompatible. Motor response elicited a motor potential (MP) and a re-afferent potential (RAP), which are both enhanced in the compatible condition.Conclusions/Significance
The present findings provide the first ACE cortical measurements of semantic processing and the motor response. N400-like effects suggest that incompatibility with motor processes interferes in sentence comprehension in a semantic fashion. Modulation of motor potentials (MP and RAP) revealed a multimodal semantic facilitation of the motor response. Both results provide neural evidence of an action-sentence bidirectional relationship. Our results suggest that ACE is not an epiphenomenal post-sentence comprehension process. In contrast, motor-language integration occurring during the verb onset supports a genuine and ongoing brain motor-language interaction. 相似文献95.
Background
Down''s syndrome (DS) is the most common genetic cause of mental retardation. Reduced number and aberrant architecture of dendritic spines are common features of DS neuropathology. However, the mechanisms involved in DS spine alterations are not known. In addition to a relevant role in synapse formation and maintenance, astrocytes can regulate spine dynamics by releasing soluble factors or by physical contact with neurons. We have previously shown impaired mitochondrial function in DS astrocytes leading to metabolic alterations in protein processing and secretion. In this study, we investigated whether deficits in astrocyte function contribute to DS spine pathology.Methodology/Principal Findings
Using a human astrocyte/rat hippocampal neuron coculture, we found that DS astrocytes are directly involved in the development of spine malformations and reduced synaptic density. We also show that thrombospondin 1 (TSP-1), an astrocyte-secreted protein, possesses a potent modulatory effect on spine number and morphology, and that both DS brains and DS astrocytes exhibit marked deficits in TSP-1 protein expression. Depletion of TSP-1 from normal astrocytes resulted in dramatic changes in spine morphology, while restoration of TSP-1 levels prevented DS astrocyte-mediated spine and synaptic alterations. Astrocyte cultures derived from TSP-1 KO mice exhibited similar deficits to support spine formation and structure than DS astrocytes.Conclusions/Significance
These results indicate that human astrocytes promote spine and synapse formation, identify astrocyte dysfunction as a significant factor of spine and synaptic pathology in the DS brain, and provide a mechanistic rationale for the exploration of TSP-1-based therapies to treat spine and synaptic pathology in DS and other neurological conditions. 相似文献96.
de Freitas JM Augusto-Pinto L Pimenta JR Bastos-Rodrigues L Gonçalves VF Teixeira SM Chiari E Junqueira AC Fernandes O Macedo AM Machado CR Pena SD 《PLoS pathogens》2006,2(3):e24
Acquisition of detailed knowledge of the structure and evolution of Trypanosoma cruzi populations is essential for control of Chagas disease. We profiled 75 strains of the parasite with five nuclear microsatellite loci, 24Salpha RNA genes, and sequence polymorphisms in the mitochondrial cytochrome oxidase subunit II gene. We also used sequences available in GenBank for the mitochondrial genes cytochrome B and NADH dehydrogenase subunit 1. A multidimensional scaling plot (MDS) based in microsatellite data divided the parasites into four clusters corresponding to T. cruzi I (MDS-cluster A), T. cruzi II (MDS-cluster C), a third group of T. cruzi strains (MDS-cluster B), and hybrid strains (MDS-cluster BH). The first two clusters matched respectively mitochondrial clades A and C, while the other two belonged to mitochondrial clade B. The 24Salpha rDNA and microsatellite profiling data were combined into multilocus genotypes that were analyzed by the haplotype reconstruction program PHASE. We identified 141 haplotypes that were clearly distributed into three haplogroups (X, Y, and Z). All strains belonging to T. cruzi I (MDS-cluster A) were Z/Z, the T. cruzi II strains (MDS-cluster C) were Y/Y, and those belonging to MDS-cluster B (unclassified T. cruzi) had X/X haplogroup genotypes. The strains grouped in the MDS-cluster BH were X/Y, confirming their hybrid character. Based on these results we propose the following minimal scenario for T. cruzi evolution. In a distant past there were at a minimum three ancestral lineages that we may call, respectively, T. cruzi I, T. cruzi II, and T. cruzi III. At least two hybridization events involving T. cruzi II and T. cruzi III produced evolutionarily viable progeny. In both events, the mitochondrial recipient (as identified by the mitochondrial clade of the hybrid strains) was T. cruzi II and the mitochondrial donor was T. cruzi III. 相似文献
97.
98.
Vast areas of southern Chile are now covered by second-growth forests because of fire and logging. To study successional patterns after moderate-intensity, anthropogenic fire disturbance, we assessed differences in soil properties and N fluxes across a chronosequence of seven successional stands (2–130 years old). We examined current predictions of successional theory concerning changes in the N cycle in forest ecosystems. Seasonal fluctuations of net N mineralization (Nmin) in surface soil and N availability (Na; Na=NH
4
+
–N+NO
3
–
–N) in upper and deep soil horizons were positively correlated with monthly precipitation. In accordance with theoretical predictions, stand age was positively, but weakly related to both Na (r
2=0.282, P<0.001) and total N (Ntot; r
2=0.192, P<0.01), and negatively related to soil C/N ratios (r
2=0.187, P<0.01) in surface soils. A weak linear increase in soil Nmin (upper plus deep soil horizons) was found across the chronosequence (r
2=0.124, P<0.022). Nmin occurred at modest rates in early successional stands, suggesting that soil disturbance did not impair microbial processes. The relationship between N fixation (Nfix) in the litter layer and stand age best fitted a quadratic model (r
2=0.228, P<0.01). In contrast to documented successional trends for most temperate, tropical and Mediterranean forests, non-symbiotic Nfix in the litter layer is a steady N input to unpolluted southern temperate forests during mid and late succession, which may compensate for hydrological losses of organic N from old-growth ecosystems. 相似文献
99.
100.